Since the invention of the first pair of in-line skates in the early 1980's, in-line skating is rapidly increasing in popularity and is successfully competing and co-existing with traditional roller skating. In fact, in-line skating has become so popular that nearly a worldwide market now purchases in-line skates. To this end, the in-line skate industry is continually developing new skates to meet the consumer's demands for lighter, faster skates.
Wheels of in-line skates are a critical component which manufacturers constantly strive to improve. Early wheels were manufactured of high friction material which resulted in prohibitively slow wheels. The industry quickly started producing the wheels from materials which had a lower coefficient of friction against the pavement and thereby created faster wheels.
In addition to demanding faster wheels, in-line skaters have another demand. In order to be suited for in-line skating, the wheels must contain a certain amount of rebound. One subjective test for rebound is to bounce a wheel on a hard surface such as a table top. If the wheel bounces, it may have desirable and suitable rebound properties for use in an in-line skate. Rebound is necessary to absorb the unevenness of pavement, loose pebbles and gravel which a skater may encounter when skating. The rebound of the wheels in part acts as a "shock absorber" for the person wearing the skates.
Currently, in-line skate wheels are produced only by the method of casting or pour molding from thermoset polyurethane. Thermoset polyurethanes are characterized by rebound suitable for use in in-line skates, however, thermoset polyurethanes are not injection moldable. Two other problems are associated with thermoset polyurethanes for in-line skate wheels. First, the material requires a 3 minute cure time which slows the manufacturing time of in-line skate wheels and raises manufacturing costs. Second, thermoset plastics are not recyclable once they have cured. That is, once a thermoset plastic has set it cannot be melted and recast and it is therefore not environmentally sound to use thermoset plastics.
Several other problems are associated with cast molding of in-line skate wheels. First, the process of cast molding is very labor-intensive. Second, cast molded wheels require machining after the wheels are molded to remove excess material. Third, besides temporal constraints, quality control problems also exist with cast wheels because air bubbles are often trapped in the cast-molded wheels. Air entrapped wheels obviously must be discarded or scrapped thus increasing production costs and creating nonrecyclable waste.
In addition to manufacturing problems, the currently available wheels are also inferior because adhesives are routinely used to bond the tread to the hub. With time and use, the adhesive breaks down causing the tread portion of the wheel to pull away from the hub. If this occurred while a skater was skating on the wheels, such an event could injure a skater.
A desirable method of manufacturing in-line skate wheels would be characterized by a method faster than the currently used cast-molding method. Such a method would also eliminate quality control problems such as air bubbles in the wheels, and further would create a safer wheel by eliminating the hub portion separating away from the tread portion. Such a method would additionally result in polyurethane wheels having necessary rebound.